aufs: ioctl, wbr_fd

Provide a file descriptor corresponding the specified writable branch.
The file descriptor will be used from user-space such as FHSM and
libau.so. For details, see aufs-util.git.
Signed-off-by: J. R. Okajima <hooanon05g@gmail.com>

fs/aufs/Makefile

@@ -17,7 +17,8 @@ aufs-y := module.o sbinfo.o super.o branch.o xino.o sysaufs.o opts.o \
 	dynop.o \
 	finfo.o file.o f_op.o \
 	dir.o vdir.o \
-	iinfo.o inode.o i_op.o i_op_add.o i_op_del.o i_op_ren.o
+	iinfo.o inode.o i_op.o i_op_add.o i_op_del.o i_op_ren.o \
+	ioctl.o
 
 # all are boolean
 aufs-$(CONFIG_PROC_FS) += procfs.o plink.o

fs/aufs/dir.c

@@ -736,6 +736,10 @@ const struct file_operations aufs_dir_fop = {
 	.llseek		= default_llseek,
 	.read		= generic_read_dir,
 	.iterate_shared	= aufs_iterate_shared,
+	.unlocked_ioctl	= aufs_ioctl_dir,
+#ifdef CONFIG_COMPAT
+	.compat_ioctl	= aufs_compat_ioctl_dir,
+#endif
 	.open		= aufs_open_dir,
 	.release	= aufs_release_dir,
 	.flush		= aufs_flush_dir,

fs/aufs/dir.h

@@ -98,5 +98,8 @@ void au_vdir_free(struct au_vdir *vdir);
 int au_vdir_init(struct file *file);
 int au_vdir_fill_de(struct file *file, struct dir_context *ctx);
 
+/* ioctl.c */
+long aufs_ioctl_dir(struct file *file, unsigned int cmd, unsigned long arg);
+
 #endif /* __KERNEL__ */
 #endif /* __AUFS_DIR_H__ */

fs/aufs/f_op.c

@@ -757,6 +757,10 @@ const struct file_operations aufs_file_fop = {
 	.read_iter	= aufs_read_iter,
 	.write_iter	= aufs_write_iter,
 
+	.unlocked_ioctl	= aufs_ioctl_nondir,
+#ifdef CONFIG_COMPAT
+	.compat_ioctl	= aufs_compat_ioctl_nondir,
+#endif
 	.mmap		= aufs_mmap,
 	.open		= aufs_open_nondir,
 	.flush		= aufs_flush_nondir,

fs/aufs/file.h

@@ -97,6 +97,15 @@ void au_fi_init_once(void *_fi);
 void au_finfo_fin(struct file *file);
 int au_finfo_init(struct file *file, struct au_fidir *fidir);
 
+/* ioctl.c */
+long aufs_ioctl_nondir(struct file *file, unsigned int cmd, unsigned long arg);
+#ifdef CONFIG_COMPAT
+long aufs_compat_ioctl_dir(struct file *file, unsigned int cmd,
+			   unsigned long arg);
+long aufs_compat_ioctl_nondir(struct file *file, unsigned int cmd,
+			      unsigned long arg);
+#endif
+
 /* ---------------------------------------------------------------------- */
 
 static inline struct au_finfo *au_fi(struct file *file)

fs/aufs/ioctl.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2005-2019 Junjiro R. Okajima
+ */
+
+/*
+ * ioctl
+ * plink-management and readdir in userspace.
+ * assist the pathconf(3) wrapper library.
+ * move-down
+ * File-based Hierarchical Storage Management.
+ */
+
+#include <linux/compat.h>
+#include <linux/file.h>
+#include "aufs.h"
+
+static int au_wbr_fd(struct path *path, struct aufs_wbr_fd __user *arg)
+{
+	int err, fd;
+	aufs_bindex_t wbi, bindex, bbot;
+	struct file *h_file;
+	struct super_block *sb;
+	struct dentry *root;
+	struct au_branch *br;
+	struct aufs_wbr_fd wbrfd = {
+		.oflags	= au_dir_roflags,
+		.brid	= -1
+	};
+	const int valid = O_RDONLY | O_NONBLOCK | O_LARGEFILE | O_DIRECTORY
+		| O_NOATIME | O_CLOEXEC;
+
+	AuDebugOn(wbrfd.oflags & ~valid);
+
+	if (arg) {
+		err = copy_from_user(&wbrfd, arg, sizeof(wbrfd));
+		if (unlikely(err)) {
+			err = -EFAULT;
+			goto out;
+		}
+
+		err = -EINVAL;
+		AuDbg("wbrfd{0%o, %d}\n", wbrfd.oflags, wbrfd.brid);
+		wbrfd.oflags |= au_dir_roflags;
+		AuDbg("0%o\n", wbrfd.oflags);
+		if (unlikely(wbrfd.oflags & ~valid))
+			goto out;
+	}
+
+	fd = get_unused_fd_flags(0);
+	err = fd;
+	if (unlikely(fd < 0))
+		goto out;
+
+	h_file = ERR_PTR(-EINVAL);
+	wbi = 0;
+	br = NULL;
+	sb = path->dentry->d_sb;
+	root = sb->s_root;
+	aufs_read_lock(root, AuLock_IR);
+	bbot = au_sbbot(sb);
+	if (wbrfd.brid >= 0) {
+		wbi = au_br_index(sb, wbrfd.brid);
+		if (unlikely(wbi < 0 || wbi > bbot))
+			goto out_unlock;
+	}
+
+	h_file = ERR_PTR(-ENOENT);
+	br = au_sbr(sb, wbi);
+	if (!au_br_writable(br->br_perm)) {
+		if (arg)
+			goto out_unlock;
+
+		bindex = wbi + 1;
+		wbi = -1;
+		for (; bindex <= bbot; bindex++) {
+			br = au_sbr(sb, bindex);
+			if (au_br_writable(br->br_perm)) {
+				wbi = bindex;
+				br = au_sbr(sb, wbi);
+				break;
+			}
+		}
+	}
+	AuDbg("wbi %d\n", wbi);
+	if (wbi >= 0)
+		h_file = au_h_open(root, wbi, wbrfd.oflags, NULL);
+
+out_unlock:
+	aufs_read_unlock(root, AuLock_IR);
+	err = PTR_ERR(h_file);
+	if (IS_ERR(h_file))
+		goto out_fd;
+
+	au_lcnt_dec(&br->br_nfiles); /* cf. au_h_open() */
+	fd_install(fd, h_file);
+	err = fd;
+	goto out; /* success */
+
+out_fd:
+	put_unused_fd(fd);
+out:
+	AuTraceErr(err);
+	return err;
+}
+
+/* ---------------------------------------------------------------------- */
+
+long aufs_ioctl_dir(struct file *file, unsigned int cmd, unsigned long arg)
+{
+	long err;
+
+	switch (cmd) {
+	case AUFS_CTL_WBR_FD:
+		err = au_wbr_fd(&file->f_path, (void __user *)arg);
+		break;
+
+	default:
+		/* do not call the lower */
+		AuDbg("0x%x\n", cmd);
+		err = -ENOTTY;
+	}
+
+	AuTraceErr(err);
+	return err;
+}
+
+long aufs_ioctl_nondir(struct file *file, unsigned int cmd, unsigned long arg)
+{
+	long err;
+
+	switch (cmd) {
+	case AUFS_CTL_WBR_FD:
+		err = au_wbr_fd(&file->f_path, (void __user *)arg);
+		break;
+
+	default:
+		/* do not call the lower */
+		AuDbg("0x%x\n", cmd);
+		err = -ENOTTY;
+	}
+
+	AuTraceErr(err);
+	return err;
+}
+
+#ifdef CONFIG_COMPAT
+long aufs_compat_ioctl_dir(struct file *file, unsigned int cmd,
+			   unsigned long arg)
+{
+	long err;
+
+	err = aufs_ioctl_dir(file, cmd, arg);
+
+	AuTraceErr(err);
+	return err;
+}
+
+long aufs_compat_ioctl_nondir(struct file *file, unsigned int cmd,
+			      unsigned long arg)
+{
+	return aufs_ioctl_nondir(file, cmd, (unsigned long)compat_ptr(arg));
+}
+#endif

include/uapi/linux/aufs_type.h

@@ -191,6 +191,30 @@ static inline int au_br_wh_linkable(int brperm)
 
 /* ---------------------------------------------------------------------- */
 
+/* ioctl */
+enum {
+	AuCtl_WBR_FD	/* pathconf wrapper */
+};
+
+/* borrowed from linux/include/linux/kernel.h */
+#ifndef ALIGN
+#define ALIGN(x, a)		__ALIGN_MASK(x, (typeof(x))(a)-1)
+#define __ALIGN_MASK(x, mask)	(((x)+(mask))&~(mask))
+#endif
+
+/* borrowed from linux/include/linux/compiler-gcc3.h */
+#ifndef __aligned
+#define __aligned(x)			__attribute__((aligned(x)))
+#endif
+
+#ifdef __KERNEL__
+#ifndef __packed
+#define __packed			__attribute__((packed))
+#endif
+#endif
+
+/* ---------------------------------------------------------------------- */
+
 /* dirren. the branch is identified by the filename who contains this */
 struct au_drinfo {
 	uint64_t ino;
@@ -210,4 +234,17 @@ struct au_drinfo_fdata {
 /* future */
 #define AUFS_DRINFO_MAGIC_V2	('a' << 24 | 'd' << 16 | 'r' << 8 | 0x02)
 
+/* ---------------------------------------------------------------------- */
+
+struct aufs_wbr_fd {
+	uint32_t	oflags;
+	int16_t		brid;
+} __aligned(8);
+
+/* ---------------------------------------------------------------------- */
+
+#define AuCtlType		'A'
+#define AUFS_CTL_WBR_FD		_IOW(AuCtlType, AuCtl_WBR_FD, \
+				     struct aufs_wbr_fd)
+
 #endif /* __AUFS_TYPE_H__ */